Chromosomal Mutations

1. Chromosomal Mutations When Good Meiosis Goes Bad

2. Mutation Review • Mutation is any change to a cell’s DNA - most mutations are bad – some can be beneficial - mutation is required for evolution to occur • Mutations can occur randomly 1 in 100,000 replications • Mutations can be caused by mutagens

3. Gene Mutation • Mutations can occur in genes - point mutation – one nucleotide substituted for another the fat cat ate the rat the fat car ate the rat - frameshift mutation – a nucleotide is either inserted or deleted from a gene - all of the DNA triplets from the point of mutation onward are altered. deletion:the fat cat ate the rat the ftcatatet her at insertion: the fat cat ate the rat the fantca tat eth era t

4. Chromosome mutation • Chromosome mutations occur when there is an error in meiosis • chromosomes hold many genes – mutation has huge impact • can result in extra copies of entire chromosomes • can be changes to parts of chromosomes

5. Diagnosis • A karyotype is produced to examine an individual’s chromosomes - a karyotype is a picture of a person’s chromosomes as homologous pairs - allows many chromosomal mutations to be seen

6. Producing a Karyotype • Fluid is taken from the womb by amniocentesis -the fluid contains cells from the embryo -the cells are grown in a tissue culture and induced to undergo mitosis. - they are treated making them easier to see and photographed in metaphase. -pictures of homologous chromosomes are matched up and examined for mutations

8. Nondisjunction • Occurs when a tetrad fails to split in meiosis I or chromatids fail to split in meiosis II

9. More Nondisjunction • Nondisjunction causes some gametes to receive an extra copy of a chromosome – called trisomy – the zygote produced from this gamete will have 3 copies of the chromosome after fertilization - trisomy 21 causes Down Syndrome • Nondisjunction causes other gametes to receive no copies of a chromosome - called monosomy–the zygote produced from this gamete will have only one copy of the chromosome after fertilization -monosomy is usually lethal

10. Deletion • A portion of a chromosome is lost. • Deletions are responsible for many syndromes: Cri du Chat, Wolf-Hirschhorn syndrome etc…

11. Inversion • A segment of a chromosome will reverse end to end. • Most common on chromosome 9 – not harmful

12. Duplication • a segment of a chromosome is duplicated producing extra copies of genes-on a chromosome. • can have harmful effects – Pallister-Killian Syndrome • can lead to new genetic combinations - potential force for evolution

13. translocation • a part of a chromosome joins another non-homologous chromosome • non- Robertsonian (balanced) – 2 non homologous chromosomes exchange parts – not harmful • Robertsonian (unbalanced) – one chromosome gives up a part to a non-homologous chromosome – Down Syndrome

14. Normal Karyotypes Male Female

15. g Trisomy 21

16. Trisomy 18